1. Field of the Invention
The present invention relates to an active-matrix substrate constituting a liquid crystal display panel (hereinafter, referred to as an LCD panel) and a method for producing the same. More specifically, the present invention relates to an active-matrix substrate in which the uneven surface of an insulating plate due to the presence of lines and switching elements is flattened by an insulating film for flattening and pixel electrodes are provided on the flattened surface; and a method for producing the same.
2. Description of the Related Art
An LCD panel generally has a structure in which two substrates are provided so as to face each other with a required space interposed therebetween and liquid crystals are injected into the space. One of the two substrates is an active-matrix substrate and the other substrate is a counter substrate. The counter substrate can include color filters of red, green and blue, or color filters of yellow, magenta and cyan.
FIG. 6 is a circuit diagram showing the configuration of a typical LCD panel. As shown in FIG. 6, a plurality of gate bus lines 1 are arranged in a row direction as scanning lines, and a plurality of source bus lines 2 are arranged in a column direction as signal lines. A plurality of pixels 3 are provided in matrix-shaped regions formed by the orthogonal crossing of the gate bus lines 1 and the source bus lines 2. Each of the pixels 3 includes a pixel electrode 4 and a switching element 5 such as a thin-film transistor (hereinafter referred to as a TFT). The pixel 3 can include a storage capacitor 6 if necessary. A storage capacitor bus line 7 and common electrodes 8 are also shown in FIG. 6.
The plurality of gate bus lines 1, the plurality of source bus lines 2 and the pixels 3 are provided on an active-matrix substrate, and the common electrodes 8 are provided on a counter substrate.
In order to realize a high aperture ratio and high precision micro-processing in the above-described active-matrix substrate, it has been suggested that an unevenness on the surface of an insulating plate, which is caused by the gate bus lines 1, the source bus lines 2 and the switching elements 5, is eliminated by an insulating film for flattening. Then the pixel electrodes 4 may be provided in a matrix on the flattened surface.
In the active-matrix substrate having the above-described structure, a rubbing treatment is conducted after the pixel electrodes 4 are formed. In the case where foreign material attaches to a portion of the insulating film in a gap between the pixel electrodes 4 when moving into the rubbing treatment step, the pixel electrodes 4 may be short-circuited with each other. Also, in the case where an edge of the pixel electrode 4 is chipped during the rubbing treatment and the chipped edge is attached to a portion in the gap between the pixel electrodes 4, the pixel electrodes 4 may be short-circuited with each other. Or, in the case where a resist mask is inaccurately formed due to the attachment of dust or the like during the formation of the resist mask in the patterning process of the pixel electrodes 4, etch residue may remain, thereby causing the pixel electrodes 4 to be short-circuited with each other. In this case, the structural defect may be corrected, for example, by removing the short-circuited portion by laser radiation. However, this requires excess time and cost.
Although its intention is not to solve the problems described above, Japanese Laid-Open Patent Publication No. 7-20497 suggests an active matrix substrate wherein a concave portion along the circumference of each of the pixel electrodes is formed in an insulating film for flattening, and liquid crystal pixels are functionally separated from one another by coercively controlling a pretilt angle of the liquid crystal molecules.
This concave portion is formed by etching the insulating film for flattening, using a photolithography technique with a resist used as a mask. The etching is performed before the formation of the pixel electrodes.
The pixel electrodes are formed as follows. A conductive film is formed on the entire top surface of the insulating film for flattening including the above-described concave portions. Then, etching is performed by a photolithography technique with a resist used as a mask.
According to this active-matrix substrate, however, the concave portion and the pixel electrodes are formed by different photolithography techniques. As a result, the number of production steps is increased and the production cost is thus increased. Also, since the pixel electrodes are formed after the formation of the concave portion in the insulating film for flattening, the number of mask alignments is increased and thus, accuracy with respect to the formation position of the pixel electrodes is deteriorated.